It's actually not about getting conduit right into a round gap - the lesser stuff fits by way of a 20mm gap anyway. It is in regards to the conduit currently being near the front fringe of the box, although the 20mm knockouts becoming Significantly even more again - ie https://fernandohzncp.bleepblogs.com/37084123/helping-the-others-realize-the-advantages-of-oval-conduit